That's a tough one. It has to accomodate movement in three dimensions (pitch roll and yaw). A flexible solution would have to resist flutter.
Shorten the gap as much as possible.
Modern tractor-trailer combos use hinged plates. Look to chain maille or segmented armor (armadillos). A chamfered nose on the trailer (like the Cybertruck) is better than a V-shape in crosswinds.
Six foot lengths of pipe insulation come in a variety of sizes.